I understand what you mean about the Trek not feeling like much of a challenge. I personally like challenge, and felt a bit disappointed with it myself, and I like Trek typically!

I took a look at a couple of the bikes on your list when I was looking. The Giant bikes weren't a very good fit for me - I'm generally short all over, and I found them too much of a stretch, even with adjustments. I also tried the Cannondale and I liked it, overall, but found that the Specialized was just a better fit for me. I found the guys at the LBS were instrumental in helping me make my decision - they adjusted the bikes, checked my positioning, and were able to point out problems with fit that I couldn't feel (yet!). When I hopped on the Tricross it just felt right, even without adjusting, and the guy fitting me even said he was surprised that it was so good a fit. If I can give you any advice, it would be to get to know the folks at the LBS and get them to give you all the fit advice they can when you try out the bikes! Happy hunting, and I hope you find your perfect fit!